1. Field of the Invention
The present invention relates to an anisotropic permanent magnet motor provided with an anisotropic permanent magnet.
2. Description of the Related Arts
Recently, an increase in output and a decrease in size of a permanent magnet motor used in a household electronic appliance have been further demanded. Also, low vibration and low noise have been demanded.
In such a circumstance, a ferrite bond magnet having a maximum energy product of about 2 MGOe (16 KJ/m3), a ferrite sintered magnet having a maximum energy product of about 5 MGOe (40 KJ/m3), or an isotropic rare-earth bond magnet having a maximum energy product of about 9 MGOe (72 KJ/m3) which has been used so far cannot satisfy such a demand. Therefore, it has been considered to use an anisotropic permanent magnet having a maximum energy product larger than those of the magnets described above.
However, a magnetic flux direction of the anisotropic permanent magnet is determined during an orientation process. Therefore, in case of orienting and magnetizing the anisotropic permanent magnet so far, radial orientation and magnetization or polar anisotropic orientation and magnetization are carried out in general.
FIG. 15 is a conceptual diagram illustrating a magnetic flux direction in case of the radial orientation (radial magnetization), and a magnetic flux direction in case of the polar anisotropic orientation (polar anisotropic magnetization) according to the related art.
In case of the radial orientation (radial magnetization), since the orientation and magnetization are just set in a radial direction, the orientation and magnetization are easily carried out. However, since the magnetic flux abruptly changes at a boundary between magnetic poles, a problem arises in that cogging torque is large.
On the other hand, in case of the polar anisotropic orientation (polar anisotropic magnetization), since the magnetic flux changes in a sine-wave shape at the boundary between the magnetic poles, it is possible to reduce the cogging torque. However, since it is necessary to set a thickness of the magnet to a half of a width of one magnetic pole, a problem arises in that the magnet is thickened to thereby cause an increase in size of the motor.
Therefore, in order to solve such problems, a technique is disclosed in, for example, WO2005/008862. WO2005/008862 discloses a motor including an anisotropic permanent magnet motor provided with a magnetic pole center magnetized in a radial direction and a boundary disposed between magnetic poles and magnetized in a polar anisotropic manner. Such a motor is capable of reducing the cogging torque and realizing an increase in torque.
However, in the technique disclosed in WO2005/008862, since the boundary between the magnetic poles is magnetized in a polar anisotropic manner, it is difficult to make the magnet thin. As a result, a problem arises in that it is difficult to realize a decrease in size and weight of the motor.